NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 11: Area Related To Circles - Exercise 11.1
Question 2

Question.  2

If the sum of the circumferences of two circles with radii \(R_1\) and \(R_2\) is equal to the circumference of a circle of radius \(R\), then

(A)

\(R_1 + R_2 = R\)

(B)

\(R_1 + R_2 > R\)

(C)

\(R_1 + R_2 < R\)

(D)

Nothing definite can be said about the relation among \(R_1, R_2\) and \(R\).

Detailed Answer with Explanation:

Step 1: Recall the formula for the circumference of a circle. Circumference (C) = \(2 \pi r\), where \(r\) is the radius (measured in metres, SI unit).

Step 2: For the first circle with radius \(R_1\), circumference = \(2 \pi R_1\).

Step 3: For the second circle with radius \(R_2\), circumference = \(2 \pi R_2\).

Step 4: The problem says the sum of these two circumferences is equal to the circumference of another circle with radius \(R\). So, \[ 2\pi R_1 + 2\pi R_2 = 2\pi R \]

Step 5: Take \(2 \pi\) common on the left side: \[ 2\pi (R_1 + R_2) = 2\pi R \]

Step 6: Cancel \(2 \pi\) from both sides (since \(2 \pi \neq 0\)): \[ R_1 + R_2 = R \]

Final Answer: The sum of the radii of the two circles is equal to the radius of the third circle. Hence, option (A) is correct.

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 11: Area Related To Circles – Exercise 11.1 | Detailed Answers